The present invention relates to an improvement of a recognition system such as a speech recognition device, more particularly, to an improvement related to the formation of feature parameters in a recognition system utilizing a specific logarithm of the filter bank output which is the feature parameter.
Conventionally, for example, when using a logarithm of a filter bank output which is the feature parameter, the following equation is applied in order to convert logarithmic values. EQU Wi=AlogPi+B
where A and B are constants, Pi is the feature parameter before the logarithm is effected, and Wi is the feature parameter after the logarithm is effected.
According to a recognition system that applies the conversion method, depending upon the character of the logarithmic curve used, if the feature parameter has a negligible value, the logarithmic output can be significantly varied even when a negligible variation is applied to the value Pi. As a result, if the feature parameter has a value near zero in a channel, this channel can be adversely affected either by internally generated electrical noise or by external noise.
In a matching device, if a variable coefficient is used, for example, via a Kalman filter as disclosed by the officially disclosed pending Japanese Patent, Tokukaisho 56-133800 "SPEECH RECOGNITION SYSTEM", when the varied coefficient drops almost to zero, its value may vary significantly, thus requiring a large number of bits for executing recognition calculations.